21 Feb 2013: Report

To Control Floods, The Dutch Turn to Nature for Inspiration

The Netherlands’ system of dikes and sea gates has long been the best in the world. But as the country confronts the challenges of climate change, it is increasingly relying on techniques that mimic natural systems and harness nature’s power to hold back the sea.

by cheryl katz

On a freezing winter day along the south-central coast of Holland, two beachcombers, hunched against the wind, stroll along a crescent of sand extending more than half a mile into the North Sea. Nearby, a snowkiter skims over the 28 million-cubic-yard heap of dredged sediment spreading along the shore. If all goes as planned, the mound will eventually disappear, rearranged by ocean currents into a 12-mile-long buffer protecting the coastline for the next two decades.

This is the Sand Engine, one of the latest innovations from Dutch masters of flood control technology and designed, as the national water board Rijkswaterstaat says, so that “nature will take the sand to the right place for us.” After having constructed the country’s vaunted system of sea gates and dikes, Dutch planners and engineers are now augmenting it with new technology enlisting nature to keep the water at bay.

“Normally, there is a lot of erosion here,” says hydraulic engineer Mathijs van Ledden, sweeping an arm toward the snow-covered spit snaking around an elongated lagoon. Van Ledden is a flood risk reduction specialist with Royal HaskoningDHV, a Dutch engineering consultancy involved in creating the Sand Engine, currently 2.2 miles wide. “This big reservoir of sand should re-nourish the rest of the coast in time,” he says, gesturing toward the skyline of The Hague, several miles away.

The Sand Engine is the signature project of Building with Nature, a consortium of Dutch industries, universities, research institutes, and public water agencies looking to harness natural systems for next-generation hydraulic engineering. Completed in late 2011 at a cost of 50 million euros ($67 million), the Sand Engine’s goal is to provide long-term fortification for eroding beaches as ocean currents gradually redistribute its dredged material. Until now, this coastline needed sand replenishment every five years, requiring expensive dredging that damaged marine ecosystems. The Sand Engine will feed beaches for about 20 years at half the price, said Marcel Stive, chair of coastal engineering at Delft University of Technology (TU Delft) and principal creator of the technology.

“At this moment, this is the safest coast we have,” Stive said. When the sand is fully spread out, it will protect 20 kilometers (12.4 miles) of shoreline from the current rate of sea-level rise, he said. If the amount of water increases, “we’ll just add more.”

With sea levels climbing — many coastal experts are projecting rises of 3 to 5 feet this century — and climate change expected to boost storm frequency and intensity, flood protection is an increasingly pressing issue worldwide. And at the forefront of flood-control technology are the Dutch, long aware of the damage that surging oceans and overflowing rivers can wreak in their low-lying country. Hydraulic engineering has been underway here since the Middle Ages, and the country’s 16.7 million residents have “dry feet” thanks to a network of dikes, canals, and engineering marvels like the Maeslant Barrier near Rotterdam: two floating gates, each the length of the Eiffel Tower, that automatically close to shield the city and its major port when a North Sea storm surge threatens.

Managing water is big business in The Netherlands: Dutch hydraulic engineers and related industries brought in around 7.5 billion euros ($10 billion) in 2008 from projects around the world, according to the most

New infrastructure must minimize environmental impacts and be adaptable to changing climate conditions.

recent figures available from the Netherlands Water Partnership. But while the Dutch export their high-tech engineering prowess worldwide — designing gigantic, mechanical structures like London’s Thames Barrier — at home the future of flood-defense encompasses a return to basics: utilizing natural materials, mimicking natural systems, and harnessing nature’s power to protect this vulnerable nation.

Projects like the Sand Engine illustrate the potential and challenges in flood-risk management, said Jos Maccabiani, a geotechnical engineer with the nonprofit applied research institute, Deltares, and program secretary of Flood Control 2015, a national initiative to improve flood management. In addition to being cost-effective, new infrastructure must minimize environmental impacts and be adaptable to changing climate conditions.

“How do you build these structures in a way that can be easily upgraded later without too much cost?” he asked. “This is a challenge that we are really working on right now.”

One solution is employing living organisms as natural buffers. A mangrove forest, for instance, “has a tendency to catch sediments and grow with sea level rise,” said Deltares marine biologist Mindert de Vries, “whereas these sandy solutions are losing sand all the time.” De Vries, an eco-engineering expert, is designing hybrid dikes, planting vegetation such as willows on the seaward side to absorb the ocean’s first blows. The dike itself can then be lower, less expensive, and more durable than a traditional dike. De Vries estimates it cuts costs around 30 percent.

“The new dikes for the new century,” he calls them. “The soft solution.”

Nature is also being recruited to turn existing dikes into ecologically enhanced “rich levees” that mimic rocky coasts, providing habitat for marine organisms. Adding roughness to the dike’s seaward face dampens waves and reduces overtopping, said Jasper Fiselier, an environmental

Nature is being recruited to turn existing dikes into ecologically enhanced levees that mimic rocky coasts.

planner with Royal HaskoningDHV and a Building with Nature project leader.

To give nature a helping hand, Dutch researchers are working on new dike materials like flexible cement to attach energy-absorbing stones, geotextiles that prevent internal erosion — a major cause of breaches — and super-strong grass that dampens wave action. One intriguing process strengthens dikes with “bio grout” produced by bacteria fed a substance that makes them excrete calcium. So far, it only works on a small scale.

The new designs provide a longer-term solution than barriers, proponents say. “If I make a [concrete] dike, and conditions change, I have to re-do the whole dike,” Fiselier said. “Whereas with a soft defense, I only have to put a half-meter [of earth] on top.”

The Netherlands is now considering a host of eco-engineered structures in a proposed 1 billion euro ($1.34 billion) package of flood-protection upgrades. Several are already in the works, including replacing the country’s tallest dike, near Hondsbossche, with a sand dune, and shoring up an aging dam in the eastern delta with a small sand engine.

The country’s first hybrid dike is now being built near Dordrecht. Incoming waves will lose power in a flooded willow forest before they reach the dike. “The dike is going to be much softer and lower, because you get the waves out,” de Vries said. “You get nature in front.” Other countries, including Singapore and Vietnam, have expressed interest in the new designs, according to de Vries.

Building with nature is a special challenge in urban areas, said Matthijs Kok, a flood-risk professor at TU Delft and a member of the environmental consulting firm HKV Consultants. His solution is multifunctional levees,

One new dike is protected by a widened beach and concealed beneath a pedestrian-friendly esplanade.

which combine ecological, recreational, and economic functions with flood control. “It sounds very easy,” Kok said, “but it’s not. Because there are so many stakeholders, so many interests.” To satisfy the various interests, businesses such as restaurants and hotels, public facilities like swimming beaches and hiking paths, and natural areas are being integrated into flood-control projects. One such example, now under construction at the seaside resort of Scheveningen, is a new dike protected by a widened beach and concealed beneath an undulating pedestrian- and bicycle-friendly esplanade.

But using nature to fight floods is not a panacea. Dunes and plants take up more room than traditional dikes. Moreover, faced with the larger storms and swollen seas predicted for the future, natural defenses may not always have enough muscle.

“Let’s be honest about it,” said van Ledden. “A forest is not going to protect you against a surge of six or eight meters [20 to 26 feet], so there are limits.”

In addition to bolstering flood defenses with enhanced natural systems, Dutch scientists and engineers also are working to “improve the decision-making when things might go wrong,” said Maccabiani.

A “Smart Dike,” which contains sensors that relay real-time status reports on the condition of the dike to decision makers.

To that end, Deltares is developing Smart Dikes — sensor-embedded levees that relay real-time status reports via cell towers to decision-makers. The purpose is to give “more time to react when you see something inside the dike that is happening while you don’t see anything on the outside yet,” Maccabiani said. Early notice of a developing problem could give time for repairs or let residents evacuate well in advance.

The system is currently in the test stage, and Maccabiani said discussions are underway with the U.S. Army Corps of Engineers and several American universities to set up a pilot project in the Mississippi delta.

Another high-tech project underway at Deltares is 3DI, which uses LIDAR, a three-dimensional laser imaging system, to map out underground water-storage capacity. The system, projected for rollout in 2014, will pinpoint flood-prone spots and places where excess water, such as runoff from heavy rains, can be accommodated.

Many areas of the U.S., including the coasts of Southern California, Florida, and New Jersey, would also benefit from natural or soft defenses, according to de Vries and others. But so far, the new designs have gotten little attention across the Atlantic. American engineers are “very much into building dikes and hard structures,” de Vries said. “And the nature people — well, these worlds don’t know each other.”

The new Dutch technology has promise, and flood management agencies in the U.S. are keeping an eye on it, said Jason Needham, a consequence specialist with the U.S. Army Corps of Engineers’ Risk-management Center in Davis, Calif., who recently spent a year in the Netherlands on a staff-exchange program. But sophisticated devices like Smart Dikes are expensive, and haven’t yet proven their worth, he said. As for natural defenses, Needham said the concepts are good, and “everyone agrees our wetlands need to be restored.”

The two countries have different approaches to flood control, Needham acknowledged, with the Dutch focusing mainly on prevention, while Americans emphasize emergency preparedness and recovery. In the face of an uncertain future climate, however, the objectives are now converging. The goal, as Needham puts it, is “how to get people safer without putting a big wall up there.”

COMMENTS

Hi Cheryl, If interested in innovations and challenges in California get in touch. We are engaged in numerous activities linking climate change mitigation and adaptation for floodplain and open coastal systems. More smart planning that Dutch heavy engineering.

Posted by
Steve Crooks
on 21 Feb 2013

It's nice to see the Dutch taking action and maintaining their leadership position in this area - not just plan forever - usually it's the U.S. with more action and less planning - of course that may be based on real the real short-term need and the natural connection between the Dutch and water - the flood of 1953 still lives in the minds of many. Unfortunately real engineering - soft and hard is still required whenever we try to cheat or fight mother nature. Perpetual planning and reactive response-based measures without proper engineering still gets you New Orleans type disasters.

Posted by
Rienk de Vries
on 27 Feb 2013

Mangroves were mentioned. I wonder of there's any known halophyte plant that is as great for barriers as mangroves that can grow on cold water? If not, then perhaps this is a legitimate target for genetic engineering.

Posted by
Roger Faulkner
on 10 Mar 2013

Excellent post.

Flood control is an important issue for the Netherlands, as about two thirds of its area is vulnerable to flooding, while the country is among the most densely populated on Earth.
Natural sand dunes and man-made dikes, dams and floodgates provide defense againststorm surges from the sea. River dikes prevent flooding from water flowing into the country by
the major rivers Rhine and Meuse, while a complicated system of drainage ditches, canals
and pumping stations (historically: windmills) keep the low lying parts dry for habitation and agriculture. Water control boards are the independent local government bodies responsible for maintaining this system.

In modern times, flood disasters coupled with technological developments have led to large construction works to reduce the influence of the sea and prevent future floods.

Historically Dikes played a crucial role in flood control in Netherlands. The first dikes were low embankments of only a metre or so in height surrounding fields to protect the crops against occasional flooding.

Around the 9th century the sea was on the advance again and many terps had to be raised to keep them safe. Many single terps had by this time grown together as villages. These were now connected by the first dikes. After 1000 AD the population grew which meant there was a greater demand of arable land but also that there was a greater workforce available and dike construction was taken up more seriously. Major contributors in later dike building were monasteries. As the largest landowners they had the organization, resources and manpower to undertake these large construction works. By 1250 most dikes had been connected into a continuous sea defense.

The next step was to move the dikes ever more seawards. Every cycle of high and low tide left a small layer of sediment. Over the years these built up to such a height that it was rarely flooded. It was then considered safe to build a new dike around this area. The old dike was often kept as a secondary defense, called sleeper dike.

A dike couldn't always be moved seawards. Especially in the southwest river delta it was often the case that the primary sea dike was undermined by a tidal channel. A secondary dike was then built, called inlaagdijk. With an inland dike, when the seaward dike collapsed the
secondary inland dike becomes the primary.

Although the redundancy provides security, the land from the first to second dike is lost- over the years the loss can become significant. Taking land from the cycle of flooding by putting a dike around it prevents it from being raised by silt left behind after a flooding. At the same time the drained soil consolidates and peat decomposes leading to land subsidence. In this way the difference between the water level on one side and land level on the other side of the dike grew. While floods became more rare, if the dike did overflow or was breached the destruction was much larger.

The construction method of dikes has changed over the centuries. Popular in the Middle Ages were 'wierdijken', earth dikes with a protective layer of seaweed. An earth embankment was cut vertically on the sea facing side. Seaweed was then stacked against this edge, held into place with poles. Compression and rotting processes resulted in a solid residue that proved very effective against wave action and needed only very little maintenance. In places where seaweed was unavailable other materials such as reeds or wicker mats were used.

Another system used much and for a long time was that of a vertical screen of timbers backed by an earth bank. Technically these vertical constructions were less successful as vibration from crashing waves and washing out of the dike foundations weakened the dike. Much damage was done to these wood constructions with the arrival of the
shipworm(Teredo navalis), a bivalve thought to
have been brought to the Netherlands by VOC
trading ships, that ate its way through Dutch sea
defenses around 1730. The change was made
from wood to using stone for reinforcement. This
was a great financial setback as there is no
natural occurring rock in the Netherlands and it
all had to be imported from abroad.

Current dikes are made with a core of sand, covered by a thick layer of clay to provide waterproofing and resistance against erosion. Dikes without a foreland have a layer of crushed rock below the waterline to slow wave action. Up to the high waterline the dike is often covered with carefully laid basalt stones or a layer of tarmac. The remainder is covered by grass and maintained by grazing sheep. Sheep keep the grass dense and compact the soil, in contrast to cattle.

The sand engine is an experiment in the management of dynamic coastline. It is run off South Holland. A sandbar-shaped peninsula was created by man the surface is about 1 km².

It is expected that this sand is then moved over the years by the action of waves, wind and currents along the coast. For the first time in 2011 at the request of theHoogheemraadschap van Delfland as part of the coastal management and the maintenance of the coastline by the highways and the province of South Holland, a peninsula was created between Ter Heijde and Kijkduin, where natural beaches and dunes are relatively narrow.

Marcel Stive may be considered as the father of this projectAnother such project could provide a solution to the weak coast betweenCamperduin and Petten, which is called the Hondsbossche seawall. The experience of this first sand engine is interesting for future projects. The construction of the sand engine at Ter Heijde cost 70 million euros and is the first in the world of its kind. Joop Atsma, State Secretary for Infrastructure and Environment, presented the project in November 2011 and his purpose was to convince that the technique of sand engine could be useful on more locations along the Dutch coast.

Dr.A.Jagadeesh Nellore(AP),India

Posted by
Dr.A.Jagadeesh
on 08 Jun 2013

Herewith we like to inform you on the international exhibition and conference WORLD WATER WORKS which toke place on 22-23th of March in Antwerp Expo. All information about the lectures is to be found throuh the website www.worldwaterworks.nl
The next edition of this event will be in Amsterdam RAI Exhibition and Coference Center on 29-30 May 2017. A contribution of Yale Environment will be very much appriciated.
Kind regards and looking forward to hear from you.
Rein van Vliet
info@worldwaterworks.nl

Posted by
rein van vliet
on 22 Jul 2016

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ABOUT THE AUTHORCheryl Katz is a science writer based in the San Francisco Bay Area. A former staff reporter for the Minneapolis Star-Tribune, the Miami Herald and the Orange County Register, she is now a freelancer specializing in stories about environmental issues and climate change. Her articles have appeared in Scientific American, Environmental Health News, and The Daily Climate, among other publications.

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